Tor Browser fails to bootstrap on IPv6-only access networks

My internet connection is IPv6-only, although DNS64+NAT64 is available.

When I try to use Tor Browser, it fails to open correctly. It also prints log messages like this:

[NOTICE] Opened Socks listener on 127.0.0.1:9150 
[WARN] Problem bootstrapping. Stuck at 5%: Connecting to directory server. (Network is unreachable; NOROUTE; count 3; recommendation warn; host x at 1.2.3.4:9001) 
[WARN] Problem bootstrapping. Stuck at 5%: Connecting to directory server. (Network is unreachable; NOROUTE; count 4; recommendation warn; host x at 2.3.4.5:443) 
[NOTICE] Closing no-longer-configured Socks listener on 127.0.0.1:9150 

Note that most (non-Tor) things work perfectly fine on my connection, as long as the application is capable of resolving AAAA records and/or connecting over AF_INET6.

I acknowledge that Tor tends not to be DNS-based (hence DNS64 doesn't help in this case). But I would expect Tor to have a list of IPv6 directory servers to try to connect to in lieu of IPv4.

Until Tor tries to connect to IPv6 directory servers, Tor Browser will be completely unusable for people on IPv6-only internet connections.

Version: Tor Browser 8.0.6 on mac OS 10.14.3.

Trac:
Username: jeremyvisser